Resumen en español En este trabajo se presentan soluciones exactas de las ecuaciones de advección-difusión y del telégrafo. Estas ecuaciones se han considerado como combinaciones de tres ecuaciones básicas, a saber: la ecuación de onda, la ecuación del transporte y la ecuación de difusión. Así, de manera natural, se introduce una tercera combinación, la ecuación de onda advectiva; la cual, a pesar de no ser muy popular, es un ejemplo sencillo y de valor didáctico, ya que permite explicar relaciones físicas y matemáticas de la superposición de las ecuaciones de transporte y ondas. Resumen en inglés In this work we present exact solutions of the advection-diffusion and the telegraph equations. These equations are considered as combinations of the basic equations: wave, heat and transport equation. Thus, in a natural way, a third combination that we called advection-wave is introduced. Although this equation is not so popular like the other combinations, it is a simple example of didactical value that allow us to explain physical and mathematical relations for the superposition of transport and wave motion.

[EN] The quantitative analysis of photosinthetic pigments in an useful tool for a better interpretation of foliar diagnosis. The easiest way to calculate them is through mathematical equations. We propose the following ones: Chl a = 10.81 Abs662 - 0.75 Abs645; Chl b = 19.02 Abs645 - 3.98 Abs662; Chl...

Resumen en inglés Background: Validated equations to measure body composition in Chilean preschool children are lacking, since the only international equation available was developed in obese, and undernourished Caucasian children. Due to the increase in overweight and obesity in Chile, it is essential to have simple and reliable instruments to assess children. Aim: To design and validate anthropometric equations to estimate body fat (BF) and total body water (TBW) to be applicable in chil (mas) dren aged 3 to 5 years, using deuterated water dilution as a reference method. Materials and Methods: Weight, height, circumferences and skinfold thickness were evaluated in 238 children aged 3 to 5 years, attending Junta Nacional de Jardines Infantiles (JUNJI). Several equations were developed using multiple regression models to estimate body water and fat. The proposed equations were validated against a sample of 77 children previously evaluated, using Bland and Alunan agreement analysis, that compares average differences of both methods with the average of predicted and estimated values. Results: New equations for TBW and BF were obtained, accounting for 86% and 72% in estimated variability. The agreement analysis showed a mean difference 0.001 ± 0.32 and 0.07 ± 0.56 kg, for TBW and BF, respectively, confirming the validity of the equations. Conclusions: The new validated equations in Chilean children aged 3 to 5 years, have an adequate and predictive capacity, especially useful for evaluating TBW and BF change in cohorts

Resumen en español La actual disponibilidad de programas de detección y tratamiento de enfermedades respiratorias en Chile ha determinado una mayor utilización de la espirometría en el diagnóstico de dichas enfermedades. La adecuada interpretación de los resultados de la espirometría requiere disponer de patrones de referencia idealmente originados en la misma población en la cual se utilizarán. Para facilitar el uso y aplicación de nuevas ecuaciones de referencia espirométricas r (mas) ecientemente modeladas en población adulta chilena, se presentan nomogramas diseñados para cada uno de los parámetros en base al género, edad y talla para sujetos entre 19 y 50 años y en mayores de 51 años. Estas ecuaciones derivan de 5 estudios nacionales que incluyeron población que cumplió criterios universales para determinar valores de referencia, (1.174 sujetos, 19 a 94 años), que efectuaron espirometrías siguiendo recomendaciones internacionales (ATS) Resumen en inglés As a result of the availability of programmes to detect and treat respiratory disease in Chile there has been a greater use of spirometry in diagnosis. To be able to correctly interpret spirometry results there must be reference patterns which, ideally come from the same population in which they will be used. In order to facilitate the use and application of new spirometric reference equations recently calculated for the adult population, there follows a series of nomogra (mas) ms. These nomograms have been designed for each of the following parameters: gender, age, and size of subjects between 19 and 50 years old and also for subjects over 51 years old. These equations are taken from 5 national studies. These studies included a population which complied with universal criteria to determine reference values ( 1.174 subjects, between 19 and 94 years old), spirometries were carried out on this population following international recommendations (ATS)

Resumen en español En este artículo, se presenta un reporte de investigación sobre el aprendizaje de las competencias matemáticas en el curso de ecuaciones diferenciales, en donde se emplea una estrategia didáctica que incorpora el uso de calculadora. El proyecto se llevó a cabo con estudiantes de la Facultad de Ingeniería, Campus Mexicali de la Universidad Autónoma de Baja California. Con el propósito de evaluar los conocimientos matemáticos se aplicó un Pre-Test y un Post-Test. (mas) Se seleccionó un grupo experimental en el cual se utilizó una estrategia didáctica basada en la teoría de representación semiótica de Duval, y un grupo de control con el que se usó un enfoque de enseñanza tradicional. El balance general de la investigación respecto de la eficiencia de conocimientos favorece al grupo experimental, particularmente cuando se trata de la competencia matemática de utilización del lenguaje simbólico y formal Resumen en inglés In this paper presents a report of a research work about learning mathematical competences in the differential equations course, in which a teaching strategy that incorporates the use of a calculator. The project was carried out with students from the Faculty of Engineering, Mexicali Campus of the Universidad Autónoma de Baja California. To evalúate knowledge of mathematics a Pre-Test and Post-Test was applied. A teaching strategy based on DuvaPs semiotic representation (mas) theory was used with an experimental group of students and the traditional method used with another control group. The overall balance of the research on the efficiency of knowledge benefits the experimental group, particularly when it comes to the mathematical competencies of using symbolic and formal language

This study documents the extent to which university students utilize diverse representations and mathematical processes to interpret and respond to a set of questions that involves fundamental concepts in the study of differential equations. Results indicate that students’ idea to solve a differenti...

The canonical form theorem, applied to a certain group of symmetry transformations of certain Fuchsian equations, leads automatically to the integration of them. The result can be extended to any n-order differential equation possesing a certain pointlike group of symmetries with a maximal abelian L...

Resumen en inglés The commonly used predictive equations to calculate resting energy expenditure (REE) can yield inaccurate results. Aim: To compare measured REE, with estimated REE in normal and obese adults. To develop specific predictive equations for our population. Patients and Methods: Eight hundred sixteen women aged 18 to 74 years old with a body mass index (BMI) between 18.5 and 69.7 kg/m² and 441 men aged 18 to 71 years old with a BMI between 185 and 67.9 kg/m2 were studied. REE (mas) was measured by indirect calorimetry and fat free mass by tetrapolar bioimpedance. REE was also estimated using FAO/WHO (F/W) and Harris-Benedict (H/B) equations. Results: Measured REE in controls was 20.7 ± 1.9 and 23.6 ± 3.3 kcal/kg/day in women and men respectively. The figures for overweight women and men were 19.8 ± 1.9 and 20.0 ± 2 kcal/kg/day, for obese women and men were 18.3 ± 1.7 and 19.0 ± 1.8 kcal/kg/day and for morbidly obese women and men, were 16.9 ± 1.8 and 16.1 ± 1.7 kcal/kg/day. When REE was corrected for fat free mass, no differences between controls and different degrees of obesity, were observed. The difference between estimated and measured REE ranged from -420 to 617 kcal in women and from -400 to 900 kcal in men. The equations derived using data obtained in the present study, showed a better predictive accuracy. Conclusions: An important error was detected when REE was predicted using FAO/WHO or Harris Benedict equations, in Chilean obese subjects. Therefore these equations must be used with caution, local equations must be devised or resting energy expenditure must be measured by indirect calorimetry (Rev Méd Chile 2002; 130: 51-60)

Resumen en español El Segundo Método de Estabilidad de Lyapunov consiste en la selección de una, así llamada, Función Candidata de Lyapunov, que satisfaga ciertas condiciones que permitan su utilización en el análisis de la estabilidad de un modelo matemático sintetizado a partir de un proceso que se desee someter a la acción de una Ley de Control determinada. En el caso de los sistemas lineales es siempre posible encontrar una función cuadrática, xT Ax, que satisfaga las condicio (mas) nes requeridas. Al aplicar el Segundo Método de Lyapunov a esta función candidata, aparece un sistema matricial de ecuaciones lineales ordinarias del tipo A T P + PA = -Q, en donde P y Q son matrices nxn, definidas positivas. En este trabajo se propone la solución numérica de este sistema algebraico mediante la resolución de un sistema lineal de n² incógnitas e igual número de ecuaciones, lo cual puede ser realizado, después de algunas manipulaciones de las ecuaciones, con algún método tradicional como la Eliminación Inversa de Gauss o cualquiera de sus variantes. Se presentan aquí dos sencillos algoritmos que permiten reacomodar la ecuación matricial original en la forma convencional de un sistema de ecuaciones algebraicas, lineales y ordinarias. Resumen en inglés The Second Method of Stability of Lyapunov consists of selecting a so-called Lyapunovs Candidate Function, which satisfies certain conditions that allows its use in the stability analysis of a mathematical model synthesized from a process which it want to put under the action of a given Control Law. In the case of linear systems, it is always possible to find a quadratic function, xT Ax, that satisfies the desired conditions. When applying the Second Stability Method of (mas) Lyapunov to this candidate function, it appears a matricial system of ordinary linear equations of the type A T P + PA = -Q, where P and Q are nxn definite positive matrixes. In this work, the numeric solution of this algebraic system is proposed by solving a linear system of n2 unknown data and the same number of equations, which can be achieved, after some manipulation to the equations, with some traditional method, such as the Inverse Elimination of Gauss or any of its variants. This work shows two easy algorithms that allows re-accommodating the original matrix equation into the conventional form of a system of algebraic linear and ordinary equations.

Resumen en español Se plantea la importancia de dominar algunos conceptos y ecuaciones matemáticas para el diagnóstico médico. Se exponen las definiciones y el modo de calcular la sensibilidad, la especificidad, el valor predictivo positivo y negativo. Se brindan ejemplos de cómo estimar la probabilidad de una enfermedad de acuerdo con las pistas disponibles. Resumen en inglés It is stated the importance of having a thorough knowledge of some concepts and mathematical equations to make the medical diagnosis. The definitions and the mode of calculating sensitivity, specificity, and the positive and negative predictive value are exposed. Examples are given of how to estimate the probability of a disease according to the available clues.

Resumen en español Este artículo presenta los resultados de la investigación experimental llevada a cabo sobre el transporte hidráulico de mezclas en canales abiertos. Se investigó acerca de las mezclas no sedimentables compuestas de pulpa de papel y agua en un canal abierto de sección transversal circular. El objeto de la investigación fue determinar las pérdidas de energía debido al flujo de agua y pulpa de papel, a fin de proponer una metodología para el diseño de canales abier (mas) tos a mezclas. A causa del desarrollo experimental se construyó un montaje de laboratorio en el cual se adaptó un canal circular con pendiente variable. Como resultado se lograron obtener nuevas ecuaciones para el coeficiente de fricción de Darcy- Weisbach y el coeficiente de fricción de Manning, que relacionan estos coeficientes con las propiedades del agua, con las de la mezcla y la pendiente del canal. Con las ecuaciones obtenidas en la investigación, el autor propuso una nueva metodología para el diseño de canales que transporten mezclas de agua y pulpa de papel. Resumen en inglés This article presents the results of the carried out experimental investigation on the hydrotransport of mixtures in open channels. The author investigated non settling mixtures composed of pulp of paper and water in an open channel of circular cross section. The object of the investigation was to determine the energy losses due to the flow of water and pulp of paper and to propose a methodology for the design of open channels for mixtures. For the experimental developmen (mas) t an assembly of laboratory was built in which a circular channel with variable slope was adapted. As a result it was possible to obtain new equations for the coefficient of friction of Darcy-Weisbach and the coefficient of friction of Manning, which relate these coefficients with the properties of the water, those of the mixture and the slope of the channel. With the equations obtained in the investigation the author it proposed a new methodology for the design of channels that they transport mixtures of water and paper pulp.

Resumen en español El problema de sobreexplotación de acuíferos en México se agudiza debido a la baja eficiencia en el uso del recurso y a la contaminación de las fuentes de abastecimiento. La situación del estado de Guanajuato es grave y requiere alternativas de solución que pueden darse mediante recomendaciones de política que contribuyan a hacer más eficiente y racional el uso del vital líquido. En este trabajo se determinaron los factores que afectan el consumo de agua en los s (mas) ectores urbano, pecuario, agrícola de riego e industrial del estado, para lo cual se estimó un modelo de ecuaciones simultáneas compuesto de cuatro ecuaciones de demanda y cuatro identidades para el período 1980-2004. El análisis de los resultados muestra que la cantidad consumida de agua responde de manera inelástica a cambios en el precio, con elasticidades de -0.0150 para el sector urbano, -0.0038 para el pecuario, -0.052 para la agricultura de riego (se utilizó la cuota de mantenimiento de la infraestructura del Distrito de Riego más el efecto del costo de la energía eléctrica para uso agrícola, ya que el agua es gratuita) y -0.126 para el sector industrial. Estas elasticidades indican que el consumo de agua en los sectores urbano y pecuario es más insensible a cambios en el precio, que en el industrial y agrícola de riego. Por tanto, las políticas de administración del consumo deberán considerar aumentos en estos sectores, pues se puede reducir en 1 % la cantidad consumida de la industria y la agricultura de riego aumentando el precio del agua en 7.93 y 19.2 %. Resumen en inglés The problem of overexploitation of groundwater in Mexico is aggravated by the low efficiency in the use of the resource and the contamination of the supply sources. The situation of the state of Guanajuato is serious and requires alternatives of solution that could come about from recommendations of policy that contribute to making a more efficient and rational use of this vital liquid. In the present work the factors that affect water consumption were determined in the u (mas) rban, livestock, irrigation agriculture and industrial sectors of the state, for which a model of simultaneous equations was estimated comprised of four equations of demand and four identities for the period 1980-2004. The analysis of results show that the amount of water consumed responds inelastically to changes in price, with elasticities of -0.0150 for the urban sector, -0.0038 for the livestock sector and -0.052 for irrigation agriculture (the quota of maintenance of the infrastructure of the Irrigation District was used, plus the effect of the cost of electric energy for agricultural use, given that the water is free) and -0.126 for the industrial sector. These elasticities indicate that water consumption in the urban and livestock sectors is more insensitive to changes in price, than in the industrial and irrigation agriculture sectors. Therefore, the policies of the administration of consumption should consider increases in these sectors, given that it is possible to reducte of 1 % the amount consumed by industry and irrigation agriculture, increasing the price of water by 7.93 and 19.2 %.

32 pages, 12 figures, 2 tables.-- PACS nrs.: 03.65.Ge; 21.45.-v; 21.60.Gx; 36.40.-c.-- Printed version published Oct 2007. | A variational method based on the use of bond coordinates and of a basis set expansion described by distributed Gaussian functions (DGF) is reviewed for its applications to th...

Resumen en inglés Background: The six minute walking distance test (6MWD) is widely used to evaluate exercise capacity in several diseases due to its simplicity and low cost. Aim: To establish reference values for 6MWD in healthy Chilean individuals. Material and methods: We studied 175 healthy volunteers aged 20-80 years (98 women) with normal spirometry and without history of respiratory, cardiovascular or other diseases that could impair walking capacity. The test was performed twice wi (mas) th an interval of 30 min. Heart rate, arterial oxygen saturation (with a pulse oxymeter) and dyspnea were measured before and after the test. Results: Walking distance was 576 ± 87 m in women and 644 ± 84 m in men (p

7 pages, 3 figures.-- Book TOC available at Google Books: http://books.google.es/books?isbn=1402018258 | The contents of this book correspond to Sessions VII and VIII of the International Workshop on Instabilities and Nonequilibrium Structures which took place in Viña del Mar, Chile, in December 199...

Ponencia presentada en el XIX Congreso Internacional de Acústica (ICA2007), Madrid, 2-7 Sep 2007.-- PACS: 43.25.Yw. | In the framework of applications of power ultrasound in liquid, this paper deals with the analysis of nonlinear ultrasonic waves through a bubbly liquid. An open-field domain is assu...

This paper presents a systematic analysis of the major switched-current (SI) errors and their influence on the quantization noise shaping of SI BandPass SD Modulators (BPSDMs). Closed form equations are provided for the degradation of the signal-to-noise ratio and for the change of the notch frequen...

12 pages.-- PACS numbers: 05.70.Ln, 05.40.-a.-- Final full-text version of the paper available at: http://dx.doi.org/10.1103/PhysRevE.76.051103. | Auxiliary material available at: http://netserver.aip.org/cgi-bin/epaps?ID=E-PLEEE8-76-106710. | A simplified version of a classical problem in thermodyn...

6 pages, 3 figures.-- ArXiv pre-print available at: http://arxiv.org/abs/nlin/0002053 | Coupled complex Ginzburg–Landau equations describe generic features of the dynamics of coupled fields when they are close to a Hopf bifurcation leading to nonlinear oscillations. We study numerically this set of ...

19 pages, no figures. | We explore cosmology of intersecting braneworlds with induced gravity on the branes. We find the cosmological equations that control the evolution of a moving codimension one brane and a codimension two brane that sits at the intersection. We study the Friedmann equation at t...

7 pages.-- PACS nrs.: 03.65.Ge, 31.10.+z. | A family of equations that combines contracted Schrödinger equations of different orders is reported here. Attention is focussed on the resulting second order, third order, and fourth order of these modified-contracted Schrödinger equations. Some of these ...

Experiments are performed which demonstrate that parallel implementations of block stationary iterative methods can solve singular systems of equations in substantially less time than the sequential counteparts. Furthermore, these experiments illustrate the behavior of different partitions of matri...

Resumen en inglés Merluccius hubbsi is the fish with the largest distributional range along the Argentinian Shelf and one of the most relevant species in the diet of many top predators in the Southwest Atlantic Ocean. Predictive regression equations were calculated to estimate total length using head and pectoral girdle bones lengths and specific body measurements. The 166 specimens studied were obtained in January and February 2008 by coastal hake trawlers operating at Chubut Province, Ar (mas) gentina. Ln- transformed data gave the best fits in the equations obtained. The present study supports the use of head and pectoral girdle bones as an alternative method to identify M. hubbsi and predict its length

This paper deals with the accurate and efficient modal analysis of arbitrarily shaped waveguides whose cross section is defined by a combination of straight, circular, and/or elliptical arcs. A novel technique for considering the presence of circular and/or elliptical segments within the frame of th...

This document describes the research activities performed in the areas of antennas, scattering and wave propagation by several research groups belonging to different Universities located in Eastern Spain. These groups are working in the practical applications of efficient numerical electromagnetic m...

This paper studies the construction of geometric integrators for nonholonomic systems. We derive the nonholonomic discrete Euler-Lagrange equations in a setting which permits to deduce geometric integrators for continuous nonholonomic systems (reduced or not). The formalism is given in terms of Lie ...

The purpose of this paper is to describe geometrically discrete Lagrangian and Hamiltonian Mechanics on Lie groupoids. From a variational principle we derive the discrete Euler-Lagrange equations and we introduce a symplectic 2-section, which is preserved by the Lagrange evolution operator. In terms...

This paper studies the structure of the adjustment costs for heterogeneous labour inputs, allowing for asymmetries and interaction effects among them. To do this, I estimate Euler equations for the demands of permanent nonproduction (white collar) and production (blue collar) employees using a sampl...

4 pages, 6 figures.-- PACS nrs.: 42.65.Sf, 05.45.Jn.-- PMID: 16384058 [PubMed]. | We show that in integro-differential delayed dynamical systems, a hybrid state of simultaneous fastscale chaos and slow-scale periodicity can emerge subsequently to a sequence of Hopf bifurcations. The resulting time t...

In this paper, a novel computer-aided design (CAD) tool of complex passive microwave devices in waveguide technology is proposed. Such a tool is based on a very efficient integral-equation analysis technique that provides a full-wave characterization of discontinuities between arbitrarily shaped wav...

6 pages, 4 figures. | We study the multimode dynamics of a semiconductor laser with optical feedback operating in the low-frequency fluctuation regime. A multimode extension of the Lang–Kobayashi (LK) model shows, in agreement with experimental observations, that the low-frequency power dropouts exh...

Resumen en inglés According to the conventional formulation it is considered that the warping of a beam under torsion is free and constant among a section and the other. This consideration is unacceptable for thin walled open elements since has been shown that in these the warping is variable and originates a different state of stress of which that considers the traditional approach. Therefore, it is necessary to include these effects when it analyses restricted torsion in this structural (mas) type of elements. This paper shows a method to obtain stiffness coefficients in thin walled open beams by using the differential equations and the matrix of initial parameters presented by V. Z. Vlasov. Some initial results are presented obtained with the model proposed.

This paper presents a geometric description of Lagrangian and Hamiltonian systems on Lie affgebroids subject to affine nonholonomic constraints. We define the notion of nonholonomically constrained system, and characterize regularity conditions that guarantee that the dynamics of the system can be o...

Dedicated to Prof. Demeter Krupka in his 65th birthday.-- 11 pages.-- MSC classes: 70G50, 58F05. | In this paper we extend the geometric formalism of the Hamilton-Jacobi theory for hamiltonian mechanics to the case of classical field theories in the framework of multisymplectic geometry and Ehresman...

The definitive version is available at: http://www.agu.org/pubs/crossref/2006/2005WR004642.shtml | This paper describes two approaches for estimating sensible heat flux, using surface renewal and similarity concepts. One approach depends on a temperature structure function parameter and is valid in ...